• The Journal of the Acoustical Society of Korea
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• v.36 no.2
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• pp.89-99
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• 2017

Multi-rotor type UAV (Unmanned Aerial Vehicle)s are expanding their applications not only for military purposes but also for private industries such as aerial photography and unmanned delivery vehicles. For wider use of unmanned aerial vehicles, studies should be carried out to improve aerodynamic efficiency and reduce noise of propellers, which can be achieved based on techniques of predicting aerodynamic performance and noise in a given environment. In this study, aerodynamic and noise prediction techniques were developed for a small unmanned aerial vehicle propeller, and it was verified by comparing it with actual measurement results. Thrust and torque due to the change of r/min and the frequency spectral prediction at a given position secured the reliability of the prediction method, which provides a basis for the shape design of the propeller.

• Journal of the Korea Society of Computer and Information
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• v.25 no.3
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• pp.145-154
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• 2020

This paper proposes a corresponding bicycle fitting method through a number of clinical results and experiments, with the aim of standardizing the comprehensive bicycle fitting method with the aim of developing a system that incorporates bicycle fitting software and hardware to proceed more precisely and quickly. This bicycle fitting method can determine the value of bicycle setting for the rider through in-depth counseling, bicycle check, sophisticated body sizing and analysis, and from the bicycle adjusted to this setting, the posture and pedaling torque can be analyzed through fixed lading, which can be followed to find the most efficient setting value and optimize the bicycle to meet the needs of the rider. Such a fitting method can increase the satisfaction of bicycle riders and also be expected to prevent injury through accurate bicycle setting values. This paper can be established as a bicycle fitting technology that can be recognized even in the global market if the final bicycle fitting system is implemented as the result presented in the most concrete domestic and foreign countries.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.369-372
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• 2002

In this research, a vision system for detecting tool breakage which is hardly detected by such indirect in-process measurement method as acoustic emission, cutting torque and motor current was developed and embedded into a PC-NC system. The vision system consists of CMOS image sensors, a slit beam laser generator and an image grabber board. Slit beam laser was emitted on the tool surface to separate the tool geometry well from the various obstacles surrounding the tool. An image of tool is captured through two steps of signal processing, that is, median filtering and thresholding and then the tool is estimated normal or broken by use of change of the centroid of the captured image. An air curtain made by the jetting high-pressure air in front of the lens was devised to prevent the vision system from being contaminated by scattered coolant, cutting chips in cutting process. To embed the vision system to a Siemens PC-NC controller 840D NC, an HMI(Human Machine Interface) program was developed under the Windows 95 operating system of MMC103. The developed HMI is placed in a sub window of the main window of 840D and this program can be activated or deactivated either by a soft key on the operating panel or M codes in the NC part program. As the tool breakage is detected, the HMI program emit a command for automatic tool change or send alarm to the NC kernel. Evaluation test in a high speed tapping center showed the developed system was successful in detection of the small-radius tool breakage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.9
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• pp.1043-1048
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• 2014

As micro screws feature reduced screw lengths and pitches, the resulting clamping force diminishes because of the reduced length of the actual joints. The elements of the clamping force are material, geometry, and friction. We studied the shrinking size of the screw and the methods to improve the clamping force by changing the material. We developed a micro screw using SWCH18A and SUS XM7 materials, and obtained the precision and thickness of the pitch through three-dimensional measurement. We also measured the external resistance of the micro screw by applying the Vicker's hardness test and conducted a break surface analysis using a break torque test and SEM for obtaining the break characteristics.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.5
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• pp.393-400
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• 2015

This paper describes the development of a chest-wearable robot that can efficiently perform self walking rehabilitation without a helper. The features of the developed robot are divided into three parts. First, as a mechanical characteristic, the conventional elbow crutch is attached at the forearm. However, the proposed robot is attached to the patient's chest, enabling them to feel free to use their hands and eliminate the burden of the arms. Second, as a characteristic of the driving algorithm, pressure sensors attached to the chest automatically perceive the patient's walking intention and move the robot-leg thereafter. Also, for safety, it stops operating when an obstacle is found in front of the patient by using ultrasonic sensors and generates a beeping sound. Finally, by using the scotch yoke mechanism, supporting legs are moved up and down using a rotary servo motor without excessive torque that is generated by large ground reaction forces. We showed that the developed robot can effectively perform self walking rehabilitation through walking experiments, and its performance was verified using Electromyograph (EMG) sensors.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.3
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• pp.189-196
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• 2018

Propeller performance measurement system for high altitude UAV was designed and applied to the wind tunnel test for 2 propeller models with a diameter around 1 m. Mechanical power of the propeller was directly measured by using the torque sensor installed on the rotating axis. The thrust of whole operation body including the propeller was measured by thrust road cell. The guide rail system was suggested to reduce the weight influence of operation body on the thrust road cell. The influence of each measured variables on the aerodynamic coefficients was studied with the repeatability and uncertainty analysis. This analysis result shows that the accuracies of the road cell and the wind velocity were major factors for the thrust coefficient. Propeller performance with typical RPM was measured with various wind speeds and the test results was summarized by performance coefficients for 5 different RPM.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.4
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• pp.662-673
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• 1997

The purpose of this study was to compare the accuracy between future impression and abutment impression using strain gauges. The master model used in this study was a partially edentulous mandibular metal cast with two fixture analogs on both sides. On the left, two future analogs were parallel, whereas right side, posterior future analog exhibiting a 15-degree lingual inclination. From master cast, 10 impressions were made for each of the three impression methods. The master frameworks was fabricated on the master model, and two-element strain gauge was attached to a master framework. The master framework was seated on each cast, and gold screws were tightened to 10 Ncm using a torque controller AI-1600 strain measurement system was used for strain measuring. Impression methods studied were : Group 1:abutment impression Group 2:fixture impression Group 3:combined impression (anterior:fixture impression, posterior:abutment impression) The results were as followed. 1. The strain values on X-axis and Y-axis according to the three impression methods showed no significant difference. 2. The strain values on parallel and angulated groups according to the three impression methods showed no significant difference. 3. The parallel group exhibited significantly higher accuracy in adaptation than angulated group for all experimental groups (p<0.05). In conclusion, it is considered that accuracy of implant prostheses is more affected by implant angulation than impression methods.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.46-58
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• 2018

A two-axis gimbal-type X-band antenna is widely used to transmit bulk image data from high-resolution observation satellites. However, undesirable microvibrations induced by driving the antenna should be attenuated, because they are a main cause of image-quality degradation of the observation satellite. In this study, a pseudoelastic memory alloy (SMA) gear was proposed to attenuate the microvibrations by driving the antenna in an azimuth angle. In addition, the proposed gear can overcome the limitations of the conventional titanium blade gear, which is not still enough and is vulnerable to plastic deformations under excessive torque. To investigate the basic characteristics of the proposed SMA mesh washer gear, a static load test was performed on the thickness of the SMA mesh washer and the rotation of the gear. Moreover, The microvibration measurement test demonstrated that the SMA mesh washer gear proposed in this study is effective for microvibration attenuation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3653-3659
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• 2015

This paper describes the reactive compatibilization of blends of a wholly aromatic thermotropic copolyester liquid crystalline polymer (TLCP) with random copolymers of ethylene and acrylic acid (EAA) and their salts. Blends were prepared by melt mixing in an intensive batch mixer, and the formation of a graft copolymer due to acidolysis between the TLCP and the acrylic acid group of the ionomer was evaluated. Chemical reaction was assessed by torque measurement during melt mixing and by thermal analysis and morphological observation. The Na-salt of the EAA ionomers was especially effective at promoting a grafting reaction. The extent of reaction depended not only on the cation, but also composition of the ionomer and reaction time. The product of the grafting reaction between the TLCP and a sodium-neutralized ionomer proved to be an effective compatibilizer for TLCP and EAA ionomers.

• Journal of Power System Engineering
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• v.6 no.1
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• pp.20-26
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• 2002

The purpose of this study is preventing the stick, scuffing, scratch between piston and cylinder in advance, and obtaining data for duration test in actual engine operation. The temperature gradient in cylinder bore according to coolant temperature were measured using $1.5{\ell}$ class diesel engine. 20 thermocouples were installed 2mm deep inside from cylinder wall near top ring of piston in cylinder block, at which points major thermal loads exist. It is suggested as proper measurement points for engine design by industrial engineers. Under full load and $70^{\circ}$, $80^{\circ}C$ and $90^{\circ}C$ coolant temperature conditions, the temperature in cylinder block and engine oil increased gradually according to the increase of coolant temperature, the siamese side temperature of top dead center is $142^{\circ}C$ in peripheral distribution, that is about $20^{\circ}C$ higher than that at thrust, anti-thrust, and rear side temperature, respectively. The maximum pressure of combustion gas in $70^{\circ}C$ coolant temperature is about 2 bar lower than those of $80^{\circ}C$ and $90^{\circ}C$ coolant temperature. The engine torque in $80^{\circ}C$, $90^{\circ}C$ coolant temperature condition is about 4.9Nm higher than that of $70^{\circ}C$ coolant temperature.